1. Field of the Invention
The present invention relates to a semiconductor memory device, and for example, relates to a semiconductor memory device that stores data by breaking a MOS (Metal-Oxide Semiconductor) capacitor gate dielectric film.
2. Related Art
To improve yield of various types of large-scale memories, redundancy is utilized. The redundancy is a technique in which a coordinate of a previously specified defective cell is stored so that the defective cell is not accessed during an actual use. To store the coordinate of the defective cell, a ROM (read-only memory) is utilized. Examples of ROMs include a memory that stores data by breaking the insulating film of a capacitor, for example. In such an insulating-film breakdown ROM, a write process (insulating-film breaking process) for storing the coordinate of a defective location can suffice only once. Storage by the insulating-film breaking process is highly reliable.
However, the conventional insulating-film breakdown ROM has vertical capacitors and diodes stacked in a vertical direction relative to a plane on which bit lines or word lines are formed. A manufacturing step of forming such capacitors and diodes piled up stereoscopically (three-dimensionally) is complicated and requires a dedicated manufacturing step. Accordingly, there is a problem in that such a conventional insulating-film breakdown ROM results in a high cost.
In a document of 2004 IEEE Custom Integrated Circuits Conference (CICC 2004), p.p. 469-472, an insulating-film breakdown ROM is formed by using a planar device. However, to constitute the insulating-film breakdown ROM, a plurality of p-type MOSFETs need to be used. In this case, the occupied area of the ROM increases.